Modern optocommunications with its extremely high transmission band widths has made the development of ever more rapid components for information processing necessary. The information, which is transmitted by means of light pulses in glass fiber cables, must be converted into an electrical signal for signal processing. This is effected with fast photodiodes whose electrical resistance changes upon irradiation with light. If an electrically-biased photodiode is illuminated with a short pulse, a voltage pulse is generated which can be further processed by an electronic circuit connected downstream thereof.
It is known from Appl. Phys. Lett. 61 (15), P. 1760-1762 that so-called MSM (metal semiconductor-metal) diodes with the smallest possible electrode spacing can be used. For this purpose a first metallically-conducting layer and a further second metallically-conducting layer are provided upon a substrate for the purpose of forming two electrodes. To optimally utilize a focussed light on the one hand and to keep the current flow region in the same conductive material as small as possible from electrode to electrode, the electrodes are configured to be planar with interdigitating finger structures. As a result, short electrode spacings of several .mu.m can be achieved whereby the switching time of such devices can then be determined substantially by the transit time of the charge carriers between the electrodes. Typical switching times with a finger spacing of 1 .mu.m lie in the magnitude range of 10-20 ps. It is however disadvantageous with such diodes that because of the lithographic resolution, there are limits to the reduction in the finger spacing so that even the achievable switching times are limited.
The elemental semiconductor silicon is characterized by good technological dominance even for its ever increasing integration density of components. On physical grounds, however, it is not possible to fabricate from it optoelectronic components like, for example, photodiodes and semiconductive lasers. On the other hand it is highly desirable to realize the most important components which will become increasingly important in the future, for optical communications technology on a basis of silicon. To date, however, the high demands on the field of data transmission have required operation with optical glass fibers with a wavelength of 1.54 .mu.m since there is an absolute minimum in the absorption. As a result, transmission rates of 10 Gbit/s can be obtained. Even the generation of such high data rates is no longer a problem today because of the use of lasers with modulators. A problem is, however, the "reading" of these large data quantities, i.e. the rapid detection of ultra-short optical pulses. Conventional photo detectors of III-IV semiconductors or also of silicon are not capable of processing these data quantities. The reading of the data forms, at this point in time, a bottleneck in the optical communication technology.